1. Field of the Invention
The present invention relates to a method and apparatus to control an optical storage device, and more particularly to a method and apparatus to control the spindle motor rotation speed of the optical storage device by detecting the armature currents of the spindle motor.
2. Description of the Prior Art
In the realm of optical storage devices there exists two major types of spindle motors. The first type is a three-phase motor, typically installed with a Hall sensor. Such motor can provide FG signal to indicate the rotation speed of the motor. Therefore the optical storage device can use the FG signal to know the current angular velocity of the motor and perform constant angular velocity (CAV) control to the motor. In addition, three-phase motors can rotate at very high speeds, so they are very popular in high-speed CD-ROM, CD-RW, and DVD-ROM applications. However, a major weakness of three-phase motors is that the motor itself, and its corresponding driving circuits, are rather expensive. Therefore, in most low-speed optical storage devices, such as DVD players and CD players, a DC motor is used as a spindle motor, so as to reduce the cost.
For optical storage devices using DC motors, there's no FG signal provided. The optical storage devices can only perform low speed constant linear velocity (CLV) control. Furthermore, because there is no easy way to sense the current angular velocity of the DC motor, it is difficult to control the deceleration rate and time before ejecting the optical medium from the optical storage device. Traditional control methods include using the optical pick-up of the optical storage device to read the timing information recorded on the optical medium, and calculating the DC motor rotation speed before performing the braking operation on the DC motor. Then, according to the calculated angular velocity of the DC motor, the system implements a constant deceleration for the corresponding period of time, causing the motor to stop spinning. Finally, the deceleration is stopped, and the ejection of the optical medium is performed. Under normal operation, this type of control method is capable of braking the medium-loaded optical storage device in a stable fashion. However, in some cases, the method will start ejection of the optical medium prior to complete deceleration of the DC motor, and cause damages to the surface of the medium. Such cases include:
1.) Erroneous calculation of the angular velocity of the DC motor. If the optical medium contains pre-existing and heavy damaged surface, the timing information recorded on the medium can not be properly read. The deceleration begins while the angular velocity of the DC motor is still unstable.
2.) Inconsistent loading of the spindle motor. For example, an 8 cm or a 12 cm optical disc, or optical discs of different thicknesses.
3.) Inherent inconsistent characteristics of the spindle motors. Same control currents applied to different spindle motors may lead to different deceleration operations.